Pacific Outer Continental Shelf Region OCS Study BOEMRE 2011-08 SPATIAL AND SEASONAL VARIATION IN THE BIOMASS AND SIZE DISTRIBUTION OF JUVENILE FISHES ASSOCIATED WITH A PETROLEUM PLATFORM OFF THE CALIFORNIA COAST, 2008-2010 Spatial and Seasonal Variation in the Biomass and Size Distribution of Juvenile Fishes Associated with a Petroleum Platform off the California Coast, 2008-2010 Authored by: Mary M. Nishimoto and Milton S. Love Submitted by: Marine Science Institute University of California Santa Barbara, CA 93106 Prepared under: MMS Cooperative Agreement No.: M08AX12732 U.S. Department of Interior Bureau of Ocean Energy Management, Regulation and Enforcement Pacific OCS Region Camarillo, CA, 93010 March 2011 Disclaimer The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the U. S. Government. Mention of trade names or commercial products does not constitute their endorsement by the U. S. Government. Availability Available for viewing and in PDF at: www.lovelab.id.ucsb.edu Bureau of Ocean Energy Management, Regulation and Enforcement Pacific OCS Region 770 Paseo Camarillo Camarillo, CA 93010 805-389-7621 Milton Love Marine Science Institute University of California Santa Barbara, CA 93106 805-893-2935 Suggested Citation Nishimoto, M. M. and M. S. Love. 2011. Spatial and Seasonal Variation in the Biomass and Size Distribution of Juvenile Fishes Associated with a Petroleum Platform off the California Coast, 2008-2010. BOEMRE OCS Study 2011-08. Marine Science Institute, University of California, Santa Barbara, California. MMS Coopera- tive Agreement No.: M08AX12732. TABLE OF CONTENTS Technical Summary v Study Products viii Spatial and Seasonal Variation in the Biomass and Size Distribution of Juvenile Fishes Associated with a Petroleum Platform off the California Coast, 2008-2010 1 Appendix 1 38 Appendix 2 62 Appendix 3 88 Appendix 4 102 Appendix 5 123 TECHNICAL SUMMARY Study Title: Spatial and Seasonal Variation in the Biomass and Size Distribution of Juvenile Fishes Associated with a Petroleum Platform off the California Coast, 2008-2010 Report Title: Spatial and Seasonal Variation in the Biomass and Size Distribution of Juvenile Fishes Associated with a Petroleum Platform off the California Coast, 2008-2010 Contract Numbers: M08AX12732 Sponsoring OCS Region: Pacific Applicable Planning Area: Central and Southern California Fiscal Years of Project Funding: 2008–2011 Completion Date of the Report: March 2011 Costs: $460,000 Cumulative Project Cost: $460,000 Principal Investigator: Milton Love Key Words: oil platforms, platforms, California, rockfishes,Sebastes , decommissioning, platform decommissioning Background and Objectives energy, or recruitment, it is important to determine if The BOEMRE defines decommissioning as the platforms provide critical habitat for early life his- process of ending oil, gas, or sulfur operations and tory stages. returning the lease or pipeline right-of-way to a con- Previous BOEMRE-supported research has estab- dition that meets the requirements of the regulations. lished that there can be extremely large numbers of The BOEMRE will conduct detailed environmental young-of-the-year (YOY) rockfishes (of several spe- reviews of any proposed decommissioning projects cies) inhabiting the midwater portions of oil platforms. to evaluate the impacts from platform removal on This research documents that 1) Some rockfish species regional fish populations. When a platform is disas- (such as bocaccio, Sebastes paucispinis) recruit at sembled, habitat is removed, and numerous fishes and far higher densities to some platforms compared to invertebrates are killed. However, yet unknown are the most natural reefs, at densities that are large enough impacts of platform removal on regional populations to later positively impact the abundance of the adult of coastal organisms, particularly the economically stock; 2) These juvenile rockfishes may be at least important rockfish species, on the Pacific Outer Con- as healthy (as measured by growth rates) as similar tinental Shelf (OCS). The assessment of the effects of fishes on natural reefs; 3) Subsurface currents likely platform activities and of the habitat created by the deliver juvenile rockfishes to the platforms at 25 m or structure of platforms on marine populations greatly deeper; 4) The timing of settlement pulses is related bears upon decommissioning issues, as questions to variability in current patterns, suggesting that the about essential fish habitat and the ecological role of offshore location and the vertical structure of plat- Pacific OCS platforms are still unresolved. forms serve an important function for recruitment (i.e., Platform decommissioning alternatives fall into settlement) of juvenile rockfishes; 5) In the absence four general categories: complete removal (the default of a platform, many of the young-of-year rockfishes option), toppling, partial removal, and leave-in-place. would not have been transported by currents to natural The suite of decommissioning alternatives that pro- reefs and would have perished before finding settle- poses to leave part or all of the abandoned platform ment habitat. structure in the marine environment is often collec- However, in order to understand the environmen- tively referred to as “rigs-to-reefs.” At this time there tal consequences of the various decommissioning are several key issues in the Pacific OCS platform alternatives on local and regional fish populations, decommissioning and reefing debate. Because fish there is a need to know the importance of the platform populations are usually limited by available habitat, as depth-stratified fish habitat when compared to ad- v jacent natural reefs of comparable depths. Platforms (b) fish recruitment to natural reefs whose crests are are structurally similar to pinnacles that steeply rise at depths of 20-35 m (the possible platform topping from the deep to shallow waters. Such natural features, depths) were surveyed using scuba to characterize the which have been shown to harbor high densities of recruiting fish assemblage that might be expected to juvenile fishes, are uncommon along the Califor- settle on a topped platform.; and (c) a novel experi- nia coast. This study was designed to evaluate the ment employing fish aggregation devices (FADs) was importance of the vertical structure of the platform designed to evaluate the importance of the shallow as settlement (i.e., recruitment) habitat for juvenile portion of platforms (<25 m) for recruitment. rockfishes, particularly in regard to a decommission- Our specific tasks in regard to the second ques- ing alternative of cutting off the top of a platform tion were to identify (a) what species recruit to and leaving a subsurface, vertical structure in place. platforms and natural reefs, and (b) the differences The primary goal of the present study is to fill and similarities of species composition, density, and gaps in information about the spatial and depth recruitment timing among platforms and natural variability in recruitment of juvenile fishes to POCS reefs. Our findings provide useful information for platforms and natural reefs off of the California coast, comparing platforms (and natural reefs) as habitat particularly in order to analyze the environmental for young rockfishes. consequences of partial platform removal on local and regional fish populations. Significant Results Visual surveys of fishes were conducted by scuba Description at seven oil platforms, seven natural reefs, and three The purpose of this study is to provide BOEMRE shipwrecks from Avila Beach, central California, with information that can be used to determine the to Long Beach, southern California, during sum- potential importance of platforms to the recruitment mer of 2008 and 2009 as scheduled for this project. and survival of depleted fish stocks. In the decommis- Sites were surveyed between one and five times in sioning process, it will be important to understand the each year. After numerous reports of relatively high role that platforms play as rockfish nursery grounds. abundances of recruiting YOY rockfishes in the Santa BOEMRE defined the following questions: Barbara Channel region in spring 2010, we revisited 1) What is the effect of depth on juvenile fish den- most of the platforms, reefs, and wrecks at least once sity, size distribution, and species composition through the summer. This study provides two lines of along the vertical structure of platforms? evidence that indicate that rockfishes likely will recruit 2) Do platforms provide critical habitat for early to platforms topped to subsurface depths between life history stages? What is the recruitment 25 and 30 m (the partial removal decommissioning value of a platform? option). The evidence is that: (1) young-of-the-year To address these information needs of BOEMRE, (YOY) rockfishes are uncommon in shallow waters at we conducted scuba surveys of the fish assemblages platforms; and (2) YOY rockfishes recruit to natural around seven platforms that represent all of the reefs and artificial structures (wrecks) that crest at various environmental parameters these structures depths comparable to where decommissioned plat- encounter. California platforms are sited in a variety forms would be topped. The implication from this of water masses, bottom depths, and distances from study that rockfishes would recruit to a number of shore. We also conducted scuba surveys on